Automatic braking device in spring motor

ABSTRACT

An automatic braking device in which a stationary cylinder is fixed to a dead shaft of a spring motor, at least two expanding brake shoes are pivoted on a rotatable drum of the motor and centrifugally operated to contact and apply frictional force to the inner surface of the stationary cylinder when the drum speed exceeds a predetermined value, and spring means for exerting return torque on the brake shoes. This braking device thus operates automatically to brake the drum and thereby absorb and dissipate kinetic energy which would otherwise cause impact.

llnitn States Patent [72] Inventors lshll-llnbnltn;

11mm: Hamlin; 'llnlmmlml lllnllrullta, all of 23%, li-Chotne, Sengoltu,MunIltyo-Iltu, Tokyo-to, Japan [21] Appl. No. 873,899 [22] Filed Nov.41, 19159 [45] Patented Dan. M, 119711 [54] AUTUMATIIQ BRAKING DEVICE11M SlPRllNG 114161710111 3 Malina, 2 Drawing Figs.

52 us. on nae/m4, 185/37 [51] llnt. 1C1 new 7/12 [50] ii leltl til/March188/180, 184; 185/37; 242/8452 R, 156

[56] lwel'elrencm Cited UNITED STATES PATENTS 1,230,560 6/1917 Camp183/184 UX 1,616,142 2/1927 Rotteretal [SS/184x 2,232,605 2/1941 Holmes188/184 X 2,685,946 8/1954 Pferd et a1. 183/184 2,829,754 4/1958Norcross 188/184 X Primary Examiner-Duane A, Reger Attorney-Holman &Stern ABSTRACT: An automatic braking device in which a stationarycylinder is fixed to a dead shaft of a spring motor, at least twoexpanding brake shoes are pivoted on a rotatable drum of the motor andcentrifugally operated to contact and apply frictional force to theinner surface of the stationary cylinder when the drum speed exceeds apredetermined value, and spring means for exerting return torque on thebrake shoes. This braking device thus operates automatically to brakethe drum and thereby absorb and dissipate kinetic energy which wouldotherwise cause impact.

Patented Dec. 14, 1971 3,627,0

INVENTORJ In, Ham/m4 Er 44.

BYgAAW M BACKGROUND OF THE INVENTION This invention relates generally tospring motors and to braking devices, and more particularly to a newautomatic braking device of a spring motor having a drum, which deviceabsorbs and dissipates impact by braking the drum at the time when themotor undergoes restoring or returning motion.

A spring motor generally has a stationary part for mounting on some basestructure and a rotatable part which can be driven by a motive-powerspring. In a common type of spring motor known heretofore, there areprovided two drums, on one of which is wound a ribbon spring in aprestressed state whereby it has a tendency to curl up or wind itselfinto a tight roll. The outer free end of this ribbon spring,constituting the above mentioned motive-power spring, is connected toand wrapped around the periphery of the other drum, constituting theabove mentioned rotatable part and herein referred to as the windupdrum.

Accordingly, when this windup drum is rotated in the direction to takeup the ribbon spring, this spring is unwound from the first drum,counter to the tendency of this spring to curl up, and exerts a returntorque on the windup drum. This return torque is utilized to sustaintension in a cord or rope or to impart windup torque to winding drums ofdevices such as route or destination indicators for displayinginformation on roll screens.

When a torque load on the windup drum or a locking force which holdsthis drum in a rotational position wherein the ribbon spring is taken upthereon is removed, the drum is caused by the spring to undergo rapidrotation, which gives rise to violent impact at the termination thereofsuch as to cause breakage of the spring and other parts and dangerousscattering of broken pieces of material. Such an impact, moreover, hasfrequently caused damage to and malfunctioning of the devices driven bythe spring motor.

SUMMARY OF THE INVENTION It is an object of the present invention toovercome the above described difficulty heretofore accompanying springmotors by providing in a spring motor an automatic braking device forbraking the drum at the time of its return rotation thereby to absorband dissipate most of the kinetic energy which would otherwise causeimpact.

Another object of the invention is to provide an automatic brakingdevice of the above-stated character which is of simple, compact, andrelatively inexpensive construction and of simple and reliableoperation.

According to the present invention, briefly summarized, there isprovided an automatic braking device of the abovestated typecharacterized by the combination of a cylindrical stationary case fixedto a stationary part of a spring motor, at least one brake shoe pivotedat one proximal end thereof on a rotatable part (drum) of the motor andhaving a friction element for contacting and applying braking resistanceto the stationary case when the rotatable part rotates at a speedexceeding a predetermined value to cause the brake shoe to pivot undercentrifugal force, and spring means to exert a return torque on thebrake shoe.

The nature, principle, details, and utility of the invention I will bemore clearly apparent from the following detailed description withrespect to a preferred embodiment of the invention when read inconjunction with the accompanying drawing, in which like parts aredesignated by like reference numerals.

BRIEF DESCRIPTION OF THE DRAWING In the drawing:

FIG. I is a side view, with parts represented in diagrammatic form withthe outer cover removed, showing the essential parts of one example of abraking device embodying the invention; and

2 FIG. 2 is a sectionalview taken along the transverse plane indicatedby line II-II in FIG. I.

DETAILED DESCRIPTION Referring to the drawing, the spring motor in whichthe automatic braking device of the invention is installed has a windupdrum ll coupled to mechanism (not shown) for driving a member to bewound such as a rope or a roll screen for displaying inscriptions (notshown). This drum I is open at one end and has a sidewall Ia, at thecenter of which there is provided a hub 9 rotatably supported on a deadshaft Ill fixed at one end thereof to a fixed structure III such as abaseplate. Thus the drum I is rotatably supported.

One end (free end) of a ribbon spring 7 is fixed to a winding part llbof the windup drum 1. This ribbon spring 7 has a tendency, impartedthereto during its production by prestressing, to curl up or wind itselfinto a tight roll] and, being anchored at its other (inner) end to aspool drum h, imparts thereto a driving torque urging the spool drum hin the arrow direction A in FIG. I.

In accordance with the present invention the windup drum 11 is providedwith an automatic brmting device which, in the illustrated example, is acentrifugal expanding brake installed within the hollow space of thedrum I and comprising, essentially, a pair of reniform brakeshoes 2, 2and a cylindrical stationary case 4 enclosed within and clear of thedrum 11. The case is fixed coaxially to the dead shaft It. Thebrakeshoes 2, 2 are in opposed positions about the shaft II with theconcave or inner sides thereof facing each other. The convex or outersides of these brakeshoes are semicircular and confront the innercylindrical wall surface of the stationary case i. The brakeshoes 2, 2have proximal ends pivoted on pivot pins 3, 3 disposed on diametricallyopposite sides of the shaft Ill and distal ends 2a, 2a constitutingweights or large-mass parts and terminating in the vicinity ofrespective pivot pins 3, 3. A tension coil spring 5 of the requiredspring force is fixed at one end thereof to a pivot pin 3 of eachbrakeshoe 2 and at the other end thereof to the distal end 2a of theother bralteshoe. Each brakeshoe 2 is further provided on its convex orouter side with an outwardly projecting brake friction element 6 of ahigh coefficient of friction fixed integrally to the brakeshoe andadapted to contact the inner surface of the stationary case 4 when thebrake shoe is moved outward by centrifugal force which overcomes theforce of the spring 5.

The braking device of the above described organization according to theinvention operates in the following manner. When a member such as a ropeor a roll screen is wound, windup drum ll coupled thereto is caused totake up ribbon spring 7, overcoming the force thereof tending to winditself into a tight roll, and is thus held. Consequently, the windupside and unwound side are maintained in a tensioned state whereby amember stretched therebetween, such as a rope, is prevented fromslackening, while a member such a roll screen is stretched in a tautstate for display without wrinkles.

When the windup side is released, or when windup drum l is releasedbecause of some cause such as a defect, the drum 1 tends to be rotatedabruptly by the force of ribbon spring 7 to cause the aforementionedundesirable results if it were not for the braking device of theinvention.

In the present mechanism as the abrupt rotation of the windup drumbegins and increases in speed, brake shoes 2, 2 are caused bycentrifugal force to pivot outward about the pivot pins 3, 3, overcomingthe forces of their respective coil springs I, 5, whereby their distalends 2a, 2a, constituting weights are swung outward, and the brakefriction elements 6, ti: contact the inner surface of stationary case d.The resulting frictional resistance to movement of the brake frictionelements b, II is imparted as a torque to the brake windup drum I andreduces its rotational speed.

When the rotational speed of the drum ll decreases, the centrifugalforce acting the brakeshoes 2, 2 decreases, and the brake frictionelements ti, 6 separate away from the inner surface of the stationarycase 4, whereupon the rotational speed of the windup drum 1 againincreases. As a result, the brakeshoes 2, 2 operate again in theabove-described manner to brake the windup drum 1 thereby to prevent itsabrupt or rapid rotation and, at the same time, to absorb the impactenergy at the final termination of the rotation.

Thus, the braking device according to the invention is installed inbuilt-in state within a windup drum of the instant type and is capableof fully controlling abrupt rotation applied to the windup drum andother windup mechanisms coupled thereto. Accordingly, impact stress dueto abrupt stopping of these mechanisms is prevented, and malfunctioningdue to breakage of the ribbon spring and damage to other mechanisms iscompletely eliminated. Furthermore, since the braking device isaccommodated compactly within the windup drum, there is no necessity ofattaching any accessory on the outside part of the entire apparatus.

We claim:

1. A spring motor comprising, in combination, a stationary structure, ashaft fixed to said stationary structure, a windup drum rotatablymounted on said shaft and comprising a transverse annular wall and acylindrical winding part fixed to the wall, a stationary cupshaped caserigidly mounted on said shaft with its cylindrical sidewall locatedclosely adjacent to the inner wall of said cylindrical winding part incoaxial relationship to the latter, at least one brakeshoe pivoted atone proximal end thereof on said transverse annular wall and having abrake friction element fixed thereto at a position other than saidproximal end, with said brake friction element being adapted to contactthe inner surface of said sidewall of the cup-shaped case to impartbraking torque to saidv windup drum when thelatter rotates at a speedexceeding a predetermined value to cause said brakeshoe to pivot undercentrifugal force, spring means to exert a return torque on thebrakeshoe tending to separate the same from said inner surface, aseparate spool drum rotatable on a stationary axis and spaced apart inparallelism to said windup drum, and a ribbon spring fixed at one end tosaid winding part of said windup drum to be wound around the windingpart and at the other end to said spool drum, and said ribbon springhaving a tendency to curl up or wind itself into a tight roll on saidspool drum thereby to impart a driving torque urging the windup drum.

2. The spring motor as claimed in claim 1, including at least twobrakeshoes each of reniform shape having a free distal end and pivotedat a proximal end thereof on a pivot pin rigidly secured on saidtransverse annular wall of the windup drum, said brakeshoes beingarranged in a circle with equal spacing and with the proximal end of onebrakeshoe confronting the distal end of the adjacent brakeshoe in thecircumferential direction, and said spring being a tension springanchored at its ends to and stretched between each pivot pin and thedistal end of the adjacent brakeshoe.

3. The spring motor as claimed in claim 1, further including a hubmember rigidly secured to said transverse annular wall of the windupdrum and rotatably mounted on said shah for rotatably supporting thewindup drum on the shaft.

lOl0l4 0066

1. A spring motor comprising, in combination, a stationary structure, a shaft fixed to said stationary structure, a windup drum rotatably mounted on said shaft and comprising a transverse annular wall and a cylindrical winding part fixed to the wall, a stationary cup-shaped case rigidly mounted on said shaft with its cylindrical sidewall located closely adjacent to the inner wall of said cylindrical winding part in coaxial relationship to the latter, at least one brakeshoe pivoted at one proximal end thereof on said transverse annular wall and having a brake friction element fixed thereto at a position other than said proximal end, with said brake friction element being adapted to contact the inner surface of said sidewall of the cup-shaped case to impart braking torque to said windup drum when the latter rotates at a speed exceeding a predetermined value to cause said brakeshoe to pivot under centrifugal force, spring means to exert a return torque on the brakeshoe tending to separate the same from said inner surface, a separate spool drum rotatable on a stationary axis and spaced apart in parallelism to said windup drum, and a ribbon spring fixed at one end to said winding part of said windup drum to be wound around the winding part and at the other end to said spool drum, and said ribbon spring having a tendency to curl up or wind itself into a tight roll on said spool drum thereby to impart a driving torque urging the windup drum.
 2. The spring motor as claimed in claim 1, including at least two brakeshoes each of reniform shape having a free distal end and pivoted at a proximal end thereof on a pivot pin rigidly secured on said transverse annular wall of the windup drum, said brakeshoes being arranged in a circle with equal spacing and with the proximal end of one brakeshoe confronting the distal end of the adjacent brakeshoe in the circumferential direction, and saiD spring being a tension spring anchored at its ends to and stretched between each pivot pin and the distal end of the adjacent brakeshoe.
 3. The spring motor as claimed in claim 1, further including a hub member rigidly secured to said transverse annular wall of the windup drum and rotatably mounted on said shaft for rotatably supporting the windup drum on the shaft. 